The present invention relates to an analytical method and apparatus which are well suited for the multifarious analyses of a granular material, such as impurities, contained in a sample, and an ultra-pure water producing and managing system which utilizes them.
There have heretofore been proposed various techniques for detecting and measuring granular materials (fine grains) which remain in ultra-pure water and various medical fluids for use in a multiplicity of fields such as semiconductors, medicines and biochemistry, and in the air and various other gases within clean rooms.
One prior-art example which is well known is a scattered light system. This system detects a granular material in such a way that a sample is irradiated with a laser beam, and the scattered light from grains is detected. In such a system, since scattered light from a medium forms the background, a large number of noise factors are involved in the measurement, and the measurement of ultramicrons is difficult.
Therefore, a variety of grain measuring systems to replace this example have been proposed.
For example, prior-art techniques disclosed in the official gazettes of Japanese Patent Laid-open No. 50-91390 (1975) and No. 52-28389 (1977) detect the concentration of a granular material in such a way that corona discharge is induced in a sample gas, thereby electrifying grains contained in the sample, and an ionic current the sense of which is reverse to the moving sense of the charged grains is detected.
Further, the inventors have recently developed a grain measuring method utilizing an photo-acoustic effect, as stated in JAPANESE JOURNAL OF APPLIED PHYSICS, Vol. 27 NO. Jun. 6, 1988, pp. L983-L985. In the grain measuring method which utilizes the photo-acoustic effect, only grains in a sample are broken down by irradiating the grains with a laser beam or the like, and the acoustic wave of a plasma generated on this occasion is detected by a piezoelectric transducer, whereby the grain sizes and numerical density of the granular material are measured on the basis of the magnitude and number of detection signals.
As another prior-art technique, an improvement on the scattered light detecting system is disclosed in the official gazette of Japanese Patent Laid-open No. 63-142234 (1988).
Among the prior-art techniques mentioned above, the system wherein the grains in the sample are electrified by corona discharge is restricted to the measurement of grains in gases, and it is not suitable for measurements concerning granular materials contained in liquid samples.
On the other hand, the photo-acoustic system already developed by the inventors gives rise to the breakdown of only the grains of the sample and, in turn, the plasma phenomenon by virtue of the light irradiation. Note should be taken of the fact that the grains in the sample exhibit a breakdown threshold value smaller than that of the medium. It is appreciated as having the advantages that the accuracy of the measurement is enhanced and that the grains can be measured irrespective of whether the sample is a gas or a liquid.
With this system based on the photo-acoustic effect, however, the internal structure of a sample cell becomes complicated because the piezoelectric transducer for converting the acoustic wave into an electrical signal is built in the cell. In addition, since a dispersion is involved in the characteristics of the individual piezoelectric transducers, means for correcting the dispersion is needed. Besides, the irradiation of the piezoelectric transducer with the laser beam causes of the degradation of the characteristics, so that a consideration therefor is needed.